Nah, what's wrong with studying it and trying to understand? It's weird how cracking open all those fancy books from classes I dozed through in school have neat stuff about fluid mechanics and thermodynamics. Who knew those stuffy old dudes with leather patches on their elbows and unkempt beards actually taught useful stuff?

Differing expansion rates as the exhaust gases cool. Bigger than 2" scavenged too much, smaller than 2" kinda choked things off. And 2.25 was the optimal diameter cat-back based on much trial and error.

You'll have to call Ted and ask him about dyno testing. I'm sure he will be happy to explain how he and others came to this conclusion based on experimentation.

Not knowing any of this, I put a 2.5" non-mandrel bent cat back on the Chili. I lost some low end. Sounded good. Wrapped out pretty well. Of course it worked out pretty well for the 5VZ swap eventually.